This invention relates to a package for a high power semiconductor laser and a method of packaging a high power semiconductor laser.
Semiconductor laser technology has matured to produce devices which are suitable for applications requiring long term, reliable laser operation. Strategies for maintaining laser stability and prolonging laser life include control of the laser operating environment. In particular, the temperature, humidity and atmosphere in which the laser operates are controlled. The preferred atmosphere taught in prior art is relatively inert with respect to the semiconductor laser materials. In particular, the art teaches that an atmosphere free of oxygen extends laser life. Also a dry atmosphere is preferred to prevent reaction with the laser materials and to preserve the integrity of the miniature electric circuitry associated with the laser operation. For a further discussion of appropriate microcircuit packaging see, "Considerations in the Hermetic Packaging of Hybrid Microcircuits", Byrnes et al., Solid State Technology, 1984. For example, an atmosphere of dry nitrogen with a helium tracer provides a favorable laser operating environment. The term dry, as used in this document, in general refers to a gaseous medium having a water content less than about 5000 ppm.
However, as semiconductor laser facet power has increased to 50 mW and higher, these generally accepted strategies for stable, long term laser operation have proved inadequate. Laser end facets, which essentially delimit the lasing cavity, can change in reflectivity and even be destroyed when a high power laser is operated in a dry helium/nitrogen atmosphere. Materials which can contaminate the container include solder flux, oils, epoxies and cleaning agents used in the process. Their presence can result in particulate and gaseous contamination reaching the surface of the facet coatings, 9 or 5 in FIG. 1, and producing impurity deposits thereon. Such deposits can change the facet reflectivity, reducing transmitted power, and increasing absorptivity at the facet which causes facet heating and eventual laser failure. Therefore, new strategies are needed to meet those laser applications which require high power together with assurance of laser stability and longevity.